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Pteranodon
Pteranodon (pronounced /tɨˈrænədɒn/; from Greek πτερ- "wing" and αν-οδων "toothless"), from the Late Cretaceous of North America(Kansas, Alabama, Nebraska, Wyoming, and South Dakota), was one of the largest pterosaur genera, with a wingspan of up to 9 metres (30 ft). Pteranodon is known from more fossil specimens than any other pterosaur, with about 1,200 specimens known to science, many of them well preserved with complete skulls and articulated skeletons, and was an important part of the animal community present in the Western Interior Seaway. Pteranodon was a reptile, but not a dinosaur. All dinosaurs are diapsid reptiles with an upright stance, and by definition Dinosauria consists of the groups Saurischia and Ornithischia, which excludes Pterosauria. While the advanced pterodactyloid pterosaurs like Pteranodon had a semi-upright stance, this evolved independently of the upright stance in dinosaurs, and pterosaurs lacked the distinctive adaptations in the hip associated with the dinosaurian posture. However, dinosaurs and pterosaurs may have been closely related, and most paleontologists place them together in the group Ornithodira, or "bird necks". Description Pteranodon was among the largest pterosaurs, with the wingspan of most adults ranging between three and six meters (9–20 ft). While most specimens are found crushed, enough fossils exist to put together a detailed description of the animal. Unlike earlier pterosaurs such as Rhamphorhynchus and Pterodactylus, Pteranodon had toothless beaks, similar to those of modern birds. Pteranodon beaks were made of solid, bony margins that projected from the base of the jaws. The beaks were long, slender, and ended in sharp points. The upper jaw was longer than the lower jaw. The upper jaw was curved upward; while this has normally been attributed only to the upward-curving beak, one specimen (UALVP 24238) has a curvature corresponding with the beak actually widening towards the tip. While the tip of the beak is not known in this specimen, the level of curvature suggests it would have been extremely long. This led Bennett (1994) to suggest that the upward curve was not entirely due to a curved beak, but rather indicated an Anhanguera-like sloping crest on the front of the beak (premaxilla). However, further specimens would be necessary to determine the actual structure of the beak in P. sternbergi. Some specimens of both P. sternbergi and P. longiceps do preserve the beak tips, and lack any premaxillary crests. The most distinctive characteristic of Pteranodon is its primary cranial crest. These crests consisted of skull bones (frontals) projecting upward and backward from the skull. The size and shape of these crests varied due to a number of factors, including age, sex, and species. Male Pteranodon sternbergi, the older species, had a more vertical crest with a broad forward projection, while their descendants, Pteranodon longiceps, evolved a narrower, more backwards-projecting crest. Females of both species were smaller, and bore small, rounded crests. See the Paleobiology section below for more on crests and their function. Other distinguishing characteristics that set Pteranodon apart from other pterosaurs include narrow neural spines on the vertebrae, plate-like bony ligaments strengthening the vertebrae above the hip, and a short tail in which the last few vertebrae are fused into a rod. There are two species of Pteranodon currently recognized as valid: Pteranodon longiceps (the type species) and Pteranodon sternbergi. The species differ only in the shape of the crest in adult males (described above), and possibly in the angle of certain skull bones. Pteranodon fossils are known from the Niobrara and Pierre Formations of the central United States. Pteranodon existed as a group for over four million years during the late Coniacian - early Campanian stages of the Cretaceous period.Bennett, S.C. (1994). "Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloida)." Occasional Papers of the Natural History Museum, University of Kansas, 169: 1-70. It is present in most layers of the Niobrarra Formation except for the upper two; in 2003, Kenneth Carpenter surveyed the distribution and dating of fossils in this formation, demonstrating that Pteranodon sternbergi existed there from 88-85 million years ago, while P. longiceps existed between 86-84.5 million years ago. A possible third species is known from the Sharon springs member of the Pierre Shale Formation in Kansas, Wyoming and South Dakota, dating to between 81.5 and 80.5 million years ago.Carpenter, K. (2003). "Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale)." High-Resolution Approaches in Stratigraphic Paleontology, 21: 421-437. DOI: 10.1007/978-1-4020-9053-0 Classification Species A number of species of Pteranodon have been named since the 1870s, though most are now considered to be junior synonyms of two or three valid species. The best-supported is the type species, P. longiceps, based on a well-preserved specimen including the first-known skull found by S.W. Williston. This individual had a wingspan of 7 mteres. Other valid species include the possibly larger P. sternbergi, with a wingspan originally estimated at 9 metres. P. occidentalis, P. velox, P. umbrosus, P. harpyia and P. comptus are considered to be nomina dubia by Bennett (1994) and others. All are probably synonymous with the more well-known Pteranodon species. ]] Pteranodon sternbergi is the only known species of Pteranodon with an upright-crest. The lower jaw of P. sternbergi was 1.25 meters (4 ft) long.Zimmerman, H., Preiss, B., and Sovak, J. (2001). Beyond the Dinosaurs!: sky dragons, sea monsters, mega-mammals, and other prehistoric beasts, Simon and Schuster. ISBN 0-689-84113-2. It was collected by George F. Sternberg in 1952 and described by John Christian Harksen in 1966, from the lower portion of the Niobrara Formation. It was older than P. longiceps and is considered by Bennett to be the direct ancestor of the later species. List of species and synonyms Because the key distinguishing characteristic Marsh noted for Pteranodon was its lack of teeth, any toothless pterosaur jaw fragment, wherever it was found in the world, tended to be attributed to Pteranodon during the late 19th and early 20th centuries. This resulted in a plethora of species and a great deal of confusion. The name became a wastebasket taxon, rather like the dinosaur Megalosaurus, to label any pterosaur remains that could not be distinguished other than by the absence of teeth. Species (often dubious ones now known to be based on sexual variation or juvenile characters) have been reclassified a number of times, and several sub-genera were erected in the seventies by Halsey Wilkinson Miller to hold them in various combinations, further confusing the taxonomy (subgenera include Longicepia, Occidentalia, and Geosternbergia). Notable authors who have discussed the various aspects of Pteranodon include Bennett, Padian, Unwin, Kellner, and Wellnhofer. Two species, P. orogensis and P. orientalis, are not actually pteranodontids and have been renamed Bennettazhia oregonensis and Bogolubovia orientalis respectively. Status of names listed below follow a survey by Bennett, 1994 unless otherwise noted. History of discovery Pteranodon was the first pterosaur found outside of Europe. Its fossils were first found by Othniel Charles Marsh in 1870, in the Late Cretaceous Smoky Hill Chalk of western Kansas. These chalk beds were deposited at the bottom of what was once the Western Interior Seaway, a large shallow sea over what is now midsection of the North American continent. These first specimens, YPM 1160 and YPM 1161, consisted of partial wing bones, as well as a tooth from the prehistoric fish Xiphactinus, which Marsh mistakenly believed to belong to his new pterosaur (all known pterosaurs up to that point had teeth). In 1871, Marsh named the find Pterodactlyus oweni, assigning it to the well-known (but much smaller) European genus Pterodactylus. Marsh also collected more wing bones of the large pterosaur in 1871. Realizing that the name Pterodactylus oweni had in 1864 already been used for a specimen of the European Pterodactylus, Marsh re-named his North American pterosaur Pterodactylus occidentalis, or "Western wing finger," in his 1872 description of the new specimen. He also named two additional species, based on size differences: Pterodactylus ingens (the largest specimen so far), and Pterodactlyus velox (the smallest). Meanwhile, Marsh's rival Edward Drinker Cope had also unearthed several specimens of the large North American pterosaur. Based on these specimens, Cope named two new species, Ornithochirus umbrosus and Ornithochirus harpyia, in an attempt to assign them to the large European genus Ornithocheirus. However, as he misspelled the name (forgetting the 'e'), he accidentally created an entirely new genus. Cope's paper naming his 'Ornithochirus'' species was published in 1872, just five days after Marsh's paper. This resulted in a dispute, fought in the published literature, over whose names had priority in what were obviously the same species. Cope conceded in 1875 that Marsh's names did have priority over his, but maintained that Pterodactylus umbrosus was a distinct species (but not genus) from any that Marsh had named previously.Cope, E.D. (1875). "The Vertebrata of the Cretaceous formations of the West." Report, U. S. Geological Survey of the Territories (Hayden), '''2: 302 pp., 57 pls. Re-evaluation by later scientists has supported Marsh's case, and found that Cope's assertion that P. umbrosus was a larger, distinct species were wrong. While the first Pteranodon wing bones were collected by Marsh and Cope in the early 1870s, the first Pteranodon skull was found on May 2, 1876, along the Smoky Hill River in Wallace County (now Logan County), Kansas, USA, by Samuel Wendell Williston, a fossil collector working for Marsh.Bennett, S.C. (2000). "Inferring stratigraphic position of fossil vertebrates from the Niobrara Chalk of western Kansas." Current Research in Earth Sciences: Kansas Geological Survey Bulletin, 244(Part 1): 26 pp. A second, smaller skull soon followed. These skulls showed that the North American pterosaur was different than any European species, in that they lacked teeth. Marsh recognized that this major difference, describing the specimens as "distinguished from all previously known genera of the order Pterosauria by the entire absence of teeth." Marsh recognized that this warranted a new genus, and he coined the name Pteranodon ("wing without tooth") in 1876. Marsh also reclassified all the previously named North American species from Pterodactylus to Pteranodon, with the larger skull, YPM 1117, referred to the new species Pteranodon longiceps.Marsh, O.C. (1876a). "Notice of a new sub-order of Pterosauria." American Journal of Science, Series 3, 11(65): 507-509. He also named an additional species, Pteranodon gracilis, based on a wing bone that he mistook for a pelvic bone. He realized his mistake, and re-classified this specimen in a separate genus, which he named Nyctosaurus.Marsh, O.C., (1876b). "Principal characters of American pterodactyls." American Journal of Science, Series 3, 12(72): 479-480. Paleobiology Diet The diet of Pteranodon is known to have included fish; fossilized fish bones have been found in the stomach area of one Pteranodon, and a fossilized fish bolus has been found between the rami of another Pteranodon, specimen AMNH 5098. Flight The wing shape of Pteranodon suggests that it would have flown rather like a modern-day albatross. This is a suggestion based on the fact that the Pteranodon had a high aspect ratio (wingspan to chord length) similar to that of the albatross — 9:1 for Pteranodon, compared to 8:1 for an albatross. Albatrosses spend long stretches of time at sea fishing, and utilize a flight pattern called "dynamic soaring" which exploits the vertical gradient of wind speed near the ocean surface to travel long distances without flapping, and without the aid of thermals (which do not occur over the open ocean the same way they do over land).Padian, K. (1983). "A functional analysis of flying and walking in pterosaurs." Paleobiology, 9'(3): 218-239. However, most scientists do agree that ''Pteranodon could flap their wings and fly with power. These two flight styles would not have been mutually exclusive in Pteranodon, or in pterosaurs in general. Crest Pteranodon was notable for its skull crest, though the function of the crest has been a subject of debate. However, most explanations have focused on the blade-like, backward pointed crest of male P. longiceps, and ignored the wide range of variation across age and gender. The fact that the crests vary so much rules out most practical functions other than for use in mating displays. George Francis Eaton, in 1910, proposed two possible functions for the crest: as an aerodynamic counterbalance, and as a muscle attachment point. He suggested that the crest might have anchored large, long jaw muscles, but admitted that this function alone could not explain the large size of some crests.Eaton, G.F. (1910). "Osteology of Pteranodon." Memoirs of the Connecticut Academy of Arts and Sciences, '''2:1-38, pls. i-xxxi. Bennett (1992) agreed with Eaton's own assessment that the crest was too large and variable to have been a muscle attachment site. Eaton had suggested that a secondary function of the crest might have been as a counterbalance against the long beak, reducing the need for heavy neck muscles to control the orientation of the head. Wind tunnel tests showed that the crest did function as an effective counterbalance to a degree, but Bennett noted that the hypothesis again focuses only on the long crests of male P. longiceps, not on the larger crests of P. sternbergi and very small crests of females. Bennett found that the crests of females had no counterbalancing effect, and that the crests of male P. sternbergi would, by themselves, have a negative effect on the balance of the head. Side to side movement of the crests would actually have required more, not less, neck musculature to control. In 1943, Dominik von Kripp suggested that the crest may have served as a rudder, an idea embraced by several later researchers.von Kripp, D. (1943). "Ein Lebensbild von Pteranodon ingens auf flugtechnischer Grundlage." Nova Acta Leopoldina, N.F., 12(83): 16-32 German. One researcher, Ross S. Stein, even suggested that the crest may have supported a membrane of skin connecting the backward-pointing crest to the neck and back, increasing its surface area and effectiveness as a rudder.Stein, R.S. (1975). "Dynamic analysis of Pteranodon ingens: a reptilian adaptation to flight." Journal of Paleontology, 49: 534-548. The rudder hypothesis again does not take into account females or P. sternbergi, which had an upward-pointing, not backward-pointing crest. Bennett also found that even in its capacity as a rudder, the crest would not provide nearly as much directional force as simply maneuvering the wings. The suggestion that the crest was an air brake, and that the animals would turn their heads to the side in order to slow down, suffers from a similar problem. Additionally, the rudder and air brake hypotheses do not explain why such large variation exists in crest size even among adults. Alexander Kellner suggested that the large crests of the pterosaur Tapejara, as well as other species, might be used for heat exchange, allowing these pterosaurs to absorb or shed heat and regulate body temperature, which would also account for the correlation between crest size and body size. However, there is no evidence of extra blood vessels in the crest for this purpose, and the large, membranous wings filled with blood vessels would have served that purpose much more effectively. With the above hypotheses ruled out, the best supported hypothesis for crest function seems to be as a sexual display. This is consistent with the size variation seen in fossil specimens, where juveniles and females have small crests and males large, elaborate, variable crests. Sexual variation Adult Pteranodon specimens can be divided into two distinct size classes, small and large, with the large size class being about one and a half times larger than the small, and the small being twice as common as the large. Both size classes lived along side each other, and while researchers had previously suggested that they represent different species, Christopher Bennett showed that the differences between them are consistent with the idea that they represent males and females, and that Pteranodon species were sexually dimorphic. Skulls from the larger size class preserve large, upwards and backward pointing crests, while the crests of the smaller size class are small and triangular. Some larger skulls also show evidence of a second crest that extended long and low along toward the tip of the beak, which is not seen in smaller specimens.Bennett, S.C. (1992). "Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests." Journal of Vertebrate Paleontology, 12(4): 422-434. The sex of the different size classes was determined not from the skulls, but from the pelvic bones. Contrary to what may be expected, the smaller size class had disproportionately large and wide-set pelvic bones. Bennett interpreted this as indicating a more spacious birth canal, through which eggs would pass. He concluded that the small size class with small, triangular crests represent females, and the larger, large-crested specimens are male. Note that the overall size and crest size also corresponds to age. Immature specimens are known from both females and males, and immature males often have small crests similar to adult females. Therefore, it seems that the large crests only developed in males when they reached their large, adult size, making the sex of immature specimens difficult to establish from partial remains.Bennett, S.C. (2001). "The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. General description of osteology." Palaeontographica, Abteilung A, 260: 1-112. The fact that females appear to have outnumbered males two to one suggests that, like modern animals with size-related sexual dimorphism such as sea lions and other pinnipeds, Pteranodon were polygynous, with a few males presiding over, and competing for, large numbers of females. Like modern pinnipeds, Pteranodon may have fought to establish territory on rocky, offshore rookeries, with the largest, and largest-crested, males gaining the most territory and having more success mating with females. The crests of male Pteranodon would not have been used in competition, but rather as "visual dominance-rank symbols", with display rituals taking the place of physical competition with other males. It is also likely that male Pteranodon played little to no part in rearing the young; such a behavior is not found in the males of modern polygynous animals. Locomotion The terrestrial locomotion of Pteranodon, especially whether it was bipedal or quadrupedal, has historically been the subject of debate. Today, most pterosaur researchers agree that pterosaurs were quadrupedal, thanks largely to the discovery of several pterosaur trackways. The possibility of swimming has been discussed briefly in two papers (Bennett 2001 and Bramwell & Whitfield 1974), and has been studied in detail at Michigan State University through the use of quantitative morphometrics and an extant phylogenetic bracket (a morphologically comparative technique invented by Larry Witmer).Bramwell, C.D. and Whitfield, G.R. (1974). "Biomechanics of Pteranodon." Philosophical Transactions Royal Society B, 267'.Smith, A.C. (2007). "Pteranodont claw morphology and its implications for aquatic locomotion." Master's Thesis, Michigan State University. Gallery References Category:Flyers Category:Twofooters Category:Dinosaurs